1. Field of the Invention
The present invention relates to a circularly polarized wave patch antenna for use with for example a mobile-satellite communication antenna.
2. Description of the Related Art
In upcoming array antennas, there will be various requirements for their performance such as beam scanning, beam forming, and low side lobing. To accomplish such requirements, active phased array antennas with LNA (low noise amplifier), HPA (high output amplifier), and a phase shifter are required. These array antenna are expected to be used for airplanes and automobiles. Thus, the array antennas including feeder circuits and so forth should be compactly and thinly formed.
In an L band mobile-satellite communication (transmission frequency=1.63 GHz, reception frequency=1.53 GHz), when signals are transmitted and received with the same antenna, a band width of 8% of frequencies for a transmission signal and a reception signal is required. When signals are transmitted and received with respective antennas, a band width of 1% of each base frequency for a transmission signal and a reception signal is required. When a signal is beamed to a stationary satellite, the signal should be scanned from the vertex by approximately 60 degrees. In the mobile-satellite communication, a circularly polarized wave antenna is also required.
When a band width of approximately 8% is accomplished for an antenna that transmits and receives signals and the dielectric constant of a dielectric substrate as a constructional member of the antenna is approximately 1.2, the thickness thereof becomes approximately 10 mm or greater. Thus, as the thickness of the substrate increases, the weight thereof also increases. Consequently, to reduce the thickness of the antenna, it is preferable to separate a transmission antenna and a reception antenna.
FIGS. 32a and 32b show an antenna that has a transmission antenna element and a reception antenna element according to a related art reference.
In FIGS. 32a and 32b, reference numerals 101 and 102 are layered dielectric substrates. A circular patch 103 is formed on the front surface of the dielectric substrate 101. A circle-annular patch 104 is formed between the dielectric substrates 101 and 102. A ground conductor 105 is formed on the rear surface of the dielectric substrate 102. A coaxial line 106 is connected from the rear surface of the dielectric substrate 102 to the patch 103 through the inside of the circle-annular patch 104. A coaxial line 107 is connected from the rear surface of the dielectric substrate 102 to the circle-annular patch 104. For example, the patches 103 and 104 are used for a transmission antenna element and a reception antenna element, respectively.
Particularly, in the antenna shown in FIGS. 32a and 32b, the antenna characteristics are deteriorated by the fringing effect of the axial line 106 that feeds a signal to the circular patch 103 against the circle-annular patch 104.
To prevent the fringing effect of the coaxial line 106 against the circle-annular patch 104, as shown in FIGS. 33a and 33b, the inner periphery of the circle-annular patch 104 is shortcircuited to the ground conductor 105 with a large number of pins 108.
The circle-annular patch 104 that is shortcircuited with the pins 108 has a larger radius than a conventional circular patch that accomplishes the same resonance frequency. Thus, when an array antenna is constructed of these antenna elements, if the element pitch necessary for a wide angle beam scanning operation is around a half-wave length, the pitch of these antenna elements is too small and thereby they cannot be properly isolated. Consequently, such an array antenna cannot provide desired antenna characteristics.
An antenna that can generate a circularly polarized wave with one point feeding has been proposed. FIGS. 34a and 34b shows the construction of this antenna. The antenna shown in FIGS. 34a and 34b comprises a circular patch 110, a ground conductor 111, a feeder line 112, and shortcircuit pins 113 and 114. It is known that the angle of the shortcircuit pin 114 and the feeder line 112 should be approximately 70 degrees to generate a circularly polarized wave in this construction. As shown in FIGS. 32a and 32b and 33a and 33b, to layer a circular patch antenna element on another antenna element, a feeder line that passes through the inside the circular patch 110 is required. In this construction, a current that flows in the circular patch 110 adversely affects the feeder line, thereby deteriorating the circularly polarized wave characteristics of the layered circular patch.